1. Field of the Invention
The present invention relates to a method of gap-filling used for fabricating a semiconductor device, and more particularly, to a gap-fill method using an amplitude modulation radiofrequency (RF) power and an apparatus for the same.
2. Discussion of the Related Art
There are many trenches and holes (or gaps) to be filled up when forming separating layer between elements, an inter metal dielectric (IMD) layer and an interlayer dielectric (ILD) layer in a fabricating process of a semiconductor device. Recently, since a density of semiconductor device increases and a width of a metal line and a distance between devices decrease, widths of the trenches and gaps decrease. As a result, there is requirement to be improved in a gap-fill process.
There are many methods for gap-filling. Among these gap-filling methods, since high aspect ratio is required, a high density plasma chemical vapor deposition (HDPCVD) method has been widely because of excellent gap-fill characteristics. In the HDPCVD method, the gaps are filled up using high density plasma.
FIG. 1 is a schematic cross-sectional view showing a conventional high density plasma chemical vapor deposition (HDPCVD) apparatus. As shown in FIG. 1, a conventional HDPCVD apparatus 10 includes a chamber 11, a susceptor 12, a gas injector 13, a RF antenna 14, a source RF power supply 15, a bias RF power supply 17 and a direct current (DC) power supply 20. The chamber 11 has an inner reactive space. An insulating plate 21, which isolates an inner space of the chamber 110 from an outer space, is disposed on an upper wall of the chamber 11. The susceptor 12 is disposed in the chamber 11. A substrate “w” is loaded on the susceptor 12. The gas injector 13 is disposed on opposite side walls of the chamber 11 and around the susceptor 12. The gas is injected into the chamber 11 through the gas injector 13. The RF antenna 14 is disposed over the chamber 11 and functions as a plasma injecting source. The RF antenna 14 is connected to the source RF power supply 15. The bias RF power supply 17, which controls an energy density of ion supplied onto the substrate “w”, is connected to the susceptor 12. Generally, a power frequency of the source RF power supply 15 may be one of 400 KHz, 2 MHz, 13.56 MHz and more than 27.12 MHz. A power frequency of the bias RF power supply 17 may be one of 13.56 MHz or less than 2 MHz. A source matching circuit 16 and a bias matching circuit 18 are respectively connected to the source RF power supply 15 and the bias RF power supply 17 to matches impedances. In addition, a direct current (DC) electrode 19 is formed in the susceptor 12 to hold the substrate to the susceptor 12 using a static electricity. The DC electrode 19 is formed of a metallic material such as tungsten (W). The DC electrode 19 is connected to a DC power supply 20.
A gap-filling process in the above-mentioned HDPCVD device 10 is explained.
A substrate “w” is loaded on a susceptor 12, and inert gases are injected into the chamber 11. And then, plasma is supplied into the chamber 11 by applying a source voltage from the source RF power supply 15 to the RF antenna 14. At this time, a reactant gas, such as silane (SiH4) and oxygen (O2), is injected onto the substrate “w” on the susceptor 12, and the bias RF power supply 17 is turned on. The reactant gas, such as silane (SiH4) and oxygen (O2), is changed into ions and active gases by colliding with electrons to depositing and etching a surface of the substrate “w”. The ions and electrons are accelerated by the bias RF power supply 17. Generally, since a depositing rate is greater than an etching rate, the reactant gas is deposited on the substrate “w”. The active gases contribute to the depositing, while the ions and electrons contribute to the etching.
When a depositing process is performed without an etching process, there are voids in the gap. FIGS. 2A to 2C are cross-sectional views showing a void formed during a gap-filling process according to the related art. As shown in FIG. 2A, a plurality of gaps “T” are formed on the substrate “w”. As shown in FIG. 2B, A material is deposited on the substrate “w” and into the plurality of gaps “T”, and an inlet of the gap is much narrow than other portions of the gap. As a material is deposited, the inlet of the gap is choked before the inner space of the gap is perfectly filled with the material, thereby forming a void in the inner space of the gap. It may be referred to as an overhang phenomenon. Other portions of the gap except for the void are filled up by the material. To avoid the overhang phenomenon, the material deposited on the substrate “w” is etched by accelerated ions during deposition of the material.
However, since a width of metal line and a distance of devices, which are referred to as a critical dimension, decrease more and more, the above method, in which a material is deposited and etched at the same time to prevent the overhang phenomenon, has it's limits to prevent the void. It is because that a by-product from etching process is deposited again in the gap, not exhausted, as the critical dimension decreases. It makes the inlet of the gap narrowed. Since pressure around the inlet of the gap is higher than that of other portions of the gap due to ions and electrons diffused to the substrate, an etched material can not be exhausted.
As a result, when the critical dimension is less than 100 nm, there are some voids in the gap even if the material on the inlet of the gap is etched.